How Do Aerosols Affect Cloudiness and Climate?

A high-resolution index suitable for multi-pollutant monitoring in urban areas

In view of the problems involved in remote sensing monitoring of urban air quality, including low spatial resolution, only for a single pollutant, complex inversion algorithms, and difficultly obtaining parameter values, in this study, a new difference smog index (DSI) was developed, and then a comparison with the normal difference haze index, the difference index, and the MODIS aerosol optical depth products. The results show that the DSI model developed in this study has a higher accuracy and a better monitoring effect in urban areas, and it has a higher resolution (30 m), which greatly improves the degree of refinement of the remote sensing monitoring. The DSI model has a higher extensibility, and it is suitable for monitoring the AQI, PM_2.5, NO₂. The DSI model proposed in this paper is simple and easy to use, and thus, it has a high potential for application and deserves promotion in urban air quality monitoring.

Dual-Wavelength High-Spectral-Resolution Lidar for Profiling Optical Properties of Aerosol and Cloud

A dual-wavelength high-spectral-resolution lidar (HSRL) based on an iodine absorption filter and a field-widened Michelson interferometer (FWMI) has been developed to profile backscatter and extinction coefficients of aerosols and clouds accurately. This instrument was tested and calibrated on multiple observations in Hangzhou and Zhoushan, respectively, from August 2018 to April 2019. This paper discusses the design and the internal calibration method of the lidar system in detail, with several typical cases of observations and the analysis of these data products. The optical properties of urban aerosols in Hangzhou and the evolvement of clouds in Zhoushan are presented, respectively.

Urban Emissions of Water Vapor in Winter

Elevated water vapor (H2Ov) mole fractions were occassionally observed downwind of Indianapolis, IN, and the Washington, D.C.-Baltimore, MD, area during airborne mass balance experiments conducted during winter months between 2012 and 2015. On days when an urban H2Ov excess signal was observed, H2Ov emissions estimates range between 1.6 × 104 and 1.7 × 105 kg s-1, and account for up to 8.4% of the total (background + urban excess) advected flow of atmospheric boundary layer H2Ov from the urban study sites. Estimates of H2Ov emissions from combustion sources and electricity generation facility cooling towers are 1-2 orders of magnitude smaller than the urban H2Ov emission rates estimated from observations. Instances of urban H2Ov enhancement could be a result of differences in snowmelt and evaporation rates within the urban area, due in part to larger wintertime anthropogenic heat flux and land cover differences, relative to surrounding rural areas. More study is needed to understand why the urban H2Ov excess signal is observed on some days, and not others. Radiative transfer modeling indicates that the observed urban enhancements in H2Ov and other greenhouse gas mole fractions contribute only 0.1°C day-1 to the urban heat island at the surface. This integrated warming through the boundary layer is offset by longwave cooling by H2Ov at the top of the boundary layer. While the radiative impacts of urban H2Ov emissions do not meaningfully influence urban heat island intensity, urban H2Ov emissions may have the potential to alter downwind aerosol and cloud properties.

10th Anniversary review: applications of analytical techniques in laboratory studies of the chemical and climatic impacts of mineral dust aerosol in the Earth's atmosphere

It is clear that mineral dust particles can impact a number of global processes including the Earth's climate through direct and indirect climate forcing, the chemical composition of the atmosphere through heterogeneous reactions, and the biogeochemistry of the oceans through dust deposition. Thus, mineral dust aerosol links land, air, and oceans in unique ways unlike any other type of atmospheric aerosol. Quantitative knowledge of how mineral dust aerosol impacts the Earth's climate, the chemical balance of the atmosphere, and the biogeochemistry of the oceans will provide a better understanding of these links and connections and the overall impact on the Earth system. Advances in the applications of analytical laboratory techniques have been critical for providing valuable information regarding these global processes. In this mini review article, we discuss examples of current and emerging techniques used in laboratory studies of mineral dust chemistry and climate and potential future directions.

Anomalous celestial polarization caused by forest fire smoke: why do some insects become visually disoriented under smoky skies?

The effects of forest fire smoke on sky polarization and animal orientation are practically unknown. Using full-sky imaging polarimetry, we therefore measured the celestial polarization pattern under a smoky sky in Fairbanks, Alaska, during the forest fire season in August 2005. It is quantitatively documented here that the celestial polarization, a sky attribute that is necessary for orientation of many polarization-sensitive animal species, above Fairbanks on 17 August 2005 was in several aspects anomalous due to the forest fire smoke: (i) The pattern of the degree of linear polarization p of the reddish smoky sky differed considerably from that of the corresponding clear blue sky. (ii) Due to the smoke, p of skylight was drastically reduced (p(max)<or=14%, p(average)<or=8%). (iii) Depending on wavelength and time, the Arago, Babinet, and Brewster neutral points of sky polarization had anomalous positions. We suggest that the disorientation of certain insects observed by Canadian researchers under smoky skies during the forest fire season in August 2003 in British Columbia was the consequence of the anomalous sky polarization caused by the forest fire smoke.